This invention relates to optoelectronic couplers, and, it relates, more particularly, to such couplers wherein the transmitter and detectors are in a stacked arrangement joined together by the optical coupling medium.
An optoelectronic coupling element or optocoupler, known and referred to as an optoisolator or optoelectronic relay, respectively, serves, to provide a device for feedback free signal transmission between two electrically separated circuits, namely a primary and a secondary circuit. Such devices typically include a luminescence diode, namely a diode that is light-emitting in the visible or infrared wavelength range (LED or IRED type), and a detector, for example a photodiode or phototransistor which are coupled together optically. The advantages of optocouplers over mechanical relays are the absence of any moving parts, their long life, small size, compatibility with semiconductor circuits, and above all their high switching frequency.
In optocouplers, the luminescence diode and photodetector are usually mounted on separator conductor areas and arranged so that as large as possible a portion of the emission radiation falls on the receiver surface of the photodetector. The optical coupling can be improved by an intermediate layer of synthetic material which brings about at the same time a stronger electric insulation.
In present conventional optocouplers, typical construction utilizes a conductive tape for the primary and secondary sides on which the transmitter and receiver chips, respectively, are applied and contacted by the usual methods. The two tapes are brought together. The light channel is produced by dabbling, cladding or sealing. Thereafter the light channel is coated with a reflecting layer and the entire component is clad or coated externally with plastic and completed. Instead of two conductor tapes, which permit the transmitter and receiver chips to be constructed opposite each other, it is also possible to use a single conductor tape method with coplanar construction of the transmitter and receiver chips.
Due to the complex design of an optoelectronic coupling element with e.g. an infrared transmitter chip, an insulating light transmission path (coupling medium) and a receiver chip, this construction is relatively costly.